1. Field of the Invention
The invention relates to a dielectric ceramic and a laminated ceramic capacitor, and more particularly, relates to a dielectric ceramic suitable for use in a thin-layer high-capacity laminated ceramic capacitor, and to a laminated ceramic capacitor made using the dielectric ceramic.
2. Description of the Related Art
As one of effective means for satisfying the needs for size reduction and higher capacity in laminated ceramic capacitors, the dielectric ceramic layers provided in the laminated ceramic capacitors are sometimes reduced in thickness. However, as the dielectric ceramic layers become thinner and thinner, the electric field intensity per dielectric ceramic layer is increased. Therefore, a higher reliability, in particular, a higher lifetime characteristics in a load test is required for the dielectric ceramic used.
BaTiO3 based dielectric ceramics are often used as the dielectric ceramics constituting dielectric ceramic layers of laminated ceramic capacitors. In order to improve the reliability and various electric properties of the BaTiO3 based dielectric ceramics, elements such as rare-earth elements and Mn have been added as accessory components.
For example, Japanese Patent Application Laid-Open No. 10-330160 (Patent Document 1) discloses, for the purpose of improving the dielectric breakdown voltage, a dielectric ceramic which has a core-shell structure and contains ABO3 (A always contains Ba, and may further contain at least one of Ca and Sr, while B always contains Ti, and may further contain at least one of Zr, Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm, and Lu) as its main component, and in the dielectric ceramic, at least one of Mn, V, Cr, Co, Ni, Fr, Nb, Mo, Ta, and W is substantially homogeneously distributed through the grains. In addition, Patent Document 1 discloses an example in which Mg is used as a shell component and Mg is distributed only in the shell portion, but not in the core.
However, even when the dielectric ceramic described in Patent Document 1 mentioned above is used, the reliability, and in particular, the lifetime characteristics in a load test, may be insufficient as the dielectric ceramic layers are further reduced in thickness, and therefore, further improvements have been desired.